论文标题
超临界柱积聚的脉冲分数流到中子星上:超X射线脉冲星的建模
Pulsed fraction of super-critical column accretion flows onto neutron stars: modeling of ultraluminous X-ray pulsars
论文作者
论文摘要
我们根据Kawashima等人的仿真结果(2016,PASJ,Pasj,68,83),我们计算超临界柱积聚的脉冲分数(PF),其中磁轴与旋转轴未对齐,其中磁轴被旋转轴未对准。在这里,我们在Schwarzschild时空中求解了地球方程,以考虑光弯曲效果。还纳入了增生柱气体运动的重力红移和相对论多普勒的效应。脉冲发射出现,因为观察到的光度超过了恒星质量黑洞的Eddington发光度,因此通过NS旋转引起的色谱柱定期变化。 PF倾向于以$θ_ {\ rm obs} $的形式增加到$θ_ {\ rm b} $,其中$θ_ {\ rm obs} $和$θ_{\ rm b} $是观察者的视角和从旋转轴的磁性轴的磁体角度。最大PF约为50%。另外,我们发现,对于$θ_ {\ rm obs} \ sillsim 5^\ circ $或$θ_ {\ rm b} \ lyseSim 5^\ circ $,PF的PF少于5%。我们的结果与对超X射线脉冲星(ULXP)的观察结果一致,但很少有例外,因为ULXPS主要显示出$ \ Lessim $ 50%的PF。我们本研究支持以下假设:ULXP由超临界柱增积力驱动到NSS上。
We calculate the pulsed fraction (PF) of the super-critical column accretion flows onto magnetized neutron stars (NSs), of which the magnetic axis is misaligned with the rotation axis, based on the simulation results by Kawashima et al.(2016, PASJ, 68, 83). Here, we solve the geodesic equation for light in the Schwarzschild spacetime in order to take into account the light bending effect. The gravitational redshift and the relativistic doppler effect from gas motions of the accretion columns are also incorporated. The pulsed emission appears since the observed luminosity, which exceeds the Eddington luminosity for the stellar-mass black holes, periodically changes via precession of the column caused by the rotation of the NS. The PF tends to increase as $θ_{\rm obs}$ approaching to $θ_{\rm B}$, where $θ_{\rm obs}$ and $θ_{\rm B}$ are the observer's viewing angle and the polar angle of the magnetic axis measured from the rotation axis. The maximum PF is around 50 %. Also, we find that the PF becomes less than 5 % for $θ_{\rm obs} \lesssim 5^\circ$ or for $θ_{\rm B} \lesssim 5^\circ$. Our results are consistent with observations of ultraluminous X-ray pulsars (ULXPs) with few exceptions, since the ULXPs mostly exhibit the PF of $\lesssim$ 50 %. Our present study supports the hypothesis that the ULXPs are powered by the super-critical column accretion onto NSs.